Means for and method of regulating the operation of electrical translation systems



2,999,669 THE OPERATION 7 Oct. 20, 1959 JACOBS MEANS FOR AND. METHOD OF REGULATING OF ELECTRICAL TRANSLATION SYSTEMS Filed Oct. 29, 1956 2 Sheets-Sheet 1 INVENTORt- JOHN E. JACOBS BY.'-

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ATTORNEY Oct. 20, 1959 .1 E JACO Filed Oct. 29, 1956 FIG. 3

2 Sheets-Sheet 2 INVENTORf-n JOHN E. JACOBS ATTORNEY MEANS FOR AND METHOD OF REGULATING THE OPERATION OF ELECTRICAL TRANSLA- TION SYSTEMS John E. Jacobs, Hales Corners, Wis., assignor to General Electric Company, a corporation of New York =Application October 29, 1956, Serial No. 618,786 9 Claims. (Cl. 250-214) The present invention relates in general to electronics, and has more particular reference to the regulation of light responsive electrical translation systems in response to ambient temperature changes, where a system monitoring photosensitive element or cell comprises material that is also sensitive to temperature variations, lwhereby to render the system substantially inert to temperature variations.

As shown, for example, in an application for U.S. Letters Patent Serial No. 494,400, filed March 15, 1955, on the invention of John E. Jacobs in Light Responsive System, crystalline photosensitive detectors, such as the sulphides or selenides of cadmium and mercury, may be employed for the control of electrical translation systems in response to variation in the intensity of light incident upon the detector, said copending application disclosing a translation system embodying a relay directly connected,

with and controlled by such a photosensitive detector for the specific purpose of controlling electric lighting systems, or other apparatus, as the intensity of incident light varies from selected levels, such as the light levels of day and night.

The crystalline sulphides and selenides of cadmium and mercury are semi-conductors having impedance characteristics which vary in response to changes in the intensity of impinging light rays, the same being disclosed, for example, in U.S. Letters Patent No. 2,706,790, No.

2,706,791, and No. 2,706,792, of April 19, 1955. These crystalline detectors, in addition to their photosensitive characteristics, are also somewhat responsive to temperature variations, and have the characteristic of increasing photosensitivity with decrease in temperature. Such thermal response characteristic will, of course, afiect the performance of any electrical translation system connected to function under the control of a crystalline detector of the character mentioned; but the characteristic ordinarily will not impair the accuracy of response of a system required merely to distinguish between the differential light intensities of day and night.

A controlled system of the character mentioned, however, maybe required to respond quite precisely to relatively small variations in the intensity of impinging light, as is the case where light sensitive detectors of the character mentioned are applied to control the automatic dimming and brightening of vehicle headlights in response to the head-on approach of another headlighted vehicle, as taught in a copending application for U.S. I Letters Patent Serial No. 385,563, filed October 12, 1953,; on the invention of John E. Jacobs in Light Responsive System. Where the controlled system is required to react precisely to relatively small light intensity variation, the desirable response characteristics of the translation system may be effected in unwanted fashion as a result of changes within the normal atmospheric temperature a range.

. An important object of the present invention, therefore, is to provide for accurately regulating a translation :system of the character mentioned in accordance with Y 2,909,669 Patented Oct. 20, 1 959 ice variations in the temperature level at which the system 'is in operation; a further object being to provide simple and inexpensive, yet positive and reliable means for regulating a light sensitive translation system in accord- 'a light responsive translation system in order to compensate for changes in the operating characteristics of the system in response to variations in temperature at which the system is required to function.

Another important object is to provide for regulating 'a translation system embodying an electron flow amplifier operable under the control of a thermally sensitive,

light responsive detector, by employing a heat sensitive element for altering the performance of the amplifier in accordance with temperature variation.

Another important object is to employ a thermistor element to regulate potential in the grid circuit of an electron flow valve forming part of a translation system for controlling the dimming and brightening of vehicle lights in response to the approach of another vehicle.

Briefly stated, the present invention contemplates an electrical translation system operable under the control of a photosensitive detector for performing any desired operation, such as the dimming and brightening of vehicle headlights, in response to changes in the intensity of light applied to the detector, as by the headlamps of an approaching vehicle, wherein the system is connected to actuate a relay switch for the accomplishment of the desired operation, and the detector comprises a light responsive semi-conductor, such as cadmium selenide or the sulphide of cadmium or mercury, having thermal as well as photo sensitivity, the system incorporating means for offsetting the effects of the thermal sensitivity of the detector, so that control of the desired operation may be accomplished with precision and only in response to intensity variations of detector impinging light rays, regardless of temperature variations. To this end, the system may incorporate an electron flow amplifier controlled by the detector for actuating the relay switch, and auxiliary control means comprising a heat sensitive thermistor and associated circuitry for variably controlling the operation of the amplifier, in accordance with prevailing temperature conditions, to thereby attain substantially constant thermal response of said system at all temperatures within its operating range.

The foregoing and numerous other important objects, advantages, and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken in connection with the accompanying drawings, discloses preferred embodiments of the invention.

Referring to the drawings:

Fig. 1 is a diagrammatic illustration of a translation system embodying the present invention; and

Figs. 2 and 3 are diagrammatic showings of modified translation systems embodying the invention.

To illustrate the invention the drawings show translation systems 11 operable under the control of a photosensitive detector 12 in order to accomplish the performance of any desired operation, such as the dimming and brightening of vehicle headlights, in response to changes in the intensity of light applied to the detector, as by the headlamps of an approaching vehicle. As shown, for example, in the aforesaid application for U.S. Letters Patent Serial No. 385,563, a vehicle headlamp commonly embodies a high or bright beam filament and a low or dim beam filament, and means may be provided for connecting one end of each of said filaments with the preferably grounded side of a suitable, preferably unidirectional electrical power source 14, such as the storage battery of an automobile, means, such as a relay switch like the switch 13, being provided for alternately connecting the ground remote ends of the high and low beam filaments with the ground remote side of the power source.

The switch 13, as'shown, may comprise a pair of stationary switch blade elements 15 and 15" adapted for connection respectively with the ground remote ends of the .high and low beam headlamp filaments, and a movable blade 16 adapted for connection with the ground remote side of the power source and yieldingly biased to normally make electrical contact with one of the stationary blades, such as the blade 15', to thereby normally energize the blade connected vehicle headlamp beam filaments from the energizing power source 14, the switch 13 being operable to shift its movable blade 16 from engagement with the blade =15 and into electrical contact with the blade 15, when the actuating coil 17 of the switch is energized, in order thus to energize the connected vehicle headlamps for bright operation and alternately to dim the same by alternately connecting and disconnecting the coil 17 from a suitable source of energizing power, such as the power source "14.

It will be seen that the switch 13 provides means for the accomplishment of a desired operation, namely, the dimming and brightening of vehicle headlamps, as switch actuating energy is supplied to or withheld from the operating coil 17; and, while the present invention is particularly well suited for application in the control of vehicle headlamps, it will, of course, be obvious that the switch '13 may be connected for the accomplishment of any other desired control function. In order to provide for the automatic control of the switch 1 3 in response to changes in the intensity of light rays applied upon the detector 12, as by the headlamps of an approaching vehicle, the translation system 11 may be rendered operative to energize the relay actuating coil 17 in accordance with changes in the intensity level of light applied on the detector 12. The translation system 11 may be and preferably is constituted to energize the coil 17 for bright beam operation of vehicle lamps when the intensity of light impinging on the detector 12 is below a selected intensity level, the coil-17 being disabled to cause low or dim beam lamp operation when the intensity of light incident upon the detector exceeds a selected lamp dimming level. The system, however, may be arranged to dim the lights when the coil "17 is energized and disable the coil for bright beam lamp operation.

The light responsive detector 12 preferably comprises crystalline cadium selenide or the sulphide of cadmium or mercury, the same being crystalline semi-conductor material of the electron donor type exhibiting the power of altering the impedance of the crystalline material as a function of the intensity of light rays impinging thereon. These materials, however, in addition to light responsive characteristics, are also somewhat sensitive to heat. Cadmium selenide, in particular, shows increasing sensitivity with decrease in temperature. Vehicle headlight control systems function to cause dimming of the headlights at a level of actuating light intensity above a selected value, and to return the lights to normal brightness when the intensity level of the system actuating light falls below a selected return-to-bright level, which is preferably ofiset substantially below the lamp dimming level. Where a detector becomes increasingly light sensitive with decrease in temperature, it will be seen that the degree of darkness required to cause the headlights to return to bright wili become progressively greater until a condition may be reached such that ordinary sky shine or the light reflected from the lamps of the vehicle in which the system is mounted will be sufiicient to lock the system in dimmed condition.

In order to provide for the automatic operation of the switch 13 in response to variation of the intensity of light applied upon the detector 12, regardless of variations in the prevailing temperature, the switch operatingtranslation system may comprise electron flow relay means V operable under the control of a thermistor T so that the response of the detector controlled system will be substantially unaffected by temperature change. As shown, the relay means V may be connected to actuate a single pole, double throw, automatically operable relay switch 18, having a pair of stationary blades 19, 19, an operating coil 20 and a movable blade or pole 21 normally biased, as by means of a spring, to yieldingly engage with one of the stationary blades, such as the blade '19. By energizing the coil 20, the pole of the relay switch may be moved out of engagement with the blade 19' and into engagement with the blade 19, which may be electrically connected with the coil 17 of the switch 13. As a consequence, the switch 13 may be actuated, as for bright beam lamp operation, whenever the coil 20 is energized to cause the pole 21 of the switch 18 to make contact with the blade 19, the switch 13 being normally biased to produce dim beam lamp operation whenever and so long as the coils 17 and 20 are disabled, by operation of the system '11 in response to the application of light on the detector 12 at lamp dimming intensity.

The blade 19 of the switch 18 may be connected with an offset component of the system 1 1 so as to adjust the sensitivity thereof at a level other than that which prevails when the pole 2 1 is in electrical contact with the blade 19 and is released from the blade 19', the purpose of such arrangement being to avoid flutter or hunting due to recycling of the system, in the event that an approaching vehicle should dim its lights and thus reduce the intensity at which the same impinge upon the detector, after the switch 1 8 shall have been actuated to dim the lights of the vehicle in which the system is mounted. The offset component also permits the system to return the lights to normal brightness at an intensity level of actuating light applied to the detector at a return-to-bright level substantially below that at which the lamps are dimmed.

In order to provide fluctuating potential electrical energy for the operation of the system 11, a transformer 22, having a primary winding connected with the power source 14 through a vibrator switch '23, may be provided for supplying alternating current electrical energy between a pair of supply conductors 24 and '25. To this end, the primary winding of the transformer may be provided with a center tap connected with one side of the power source 14, the opposite ends of the winding being electrically connected with the stationary contacts of the vibrator switch 23, the movable contact or pole of which is connected with the other side of the power source 14. The secondary winding of the transformer 22 may be provided with a grounded center tap, the opposite ends of said secondary winding being connected respectively with the AC. supply conductors 24 and 25, a buffer condenser 26 being preferably connected between said conductors, in order to absorb surges which occur upon the breaking of circuits by the vibrator switch 23.

As shown more particularly in Fig. 1 of the drawings, the normally closed switch contact 15' may be connected with the low or dim beam filaments of the vehicle lamps, the contact 15 being adapted for connection with the high or bright beam lamp filaments. The switch actuating coil 17 may be interconnected between ground and the blade 19 of the switch 18, the movable pole 21 of the switch being electrically connected with the ground remote side of the power source 14. Since said pole 21 is normally biased to a position engaging the switch blade 19' and disengaged from the switch blade 19, it will be seen that the actuating coil 17 of the switch 13 will be normally inactive with the low or dim beam lamp filaments in operation by connection thereof with the power source through the switch blade 15 normally engaged by the pole 16 of the relay switch 13. By energizing the operating coil 20 of the switch 18, its pole 21 .will be released from the blade 19' and engaged with the blade 19, to thereby energize the actuating 'coil 17, whereby to cause the switch 13 to disable the low beam lamp filaments and energize the high beam filaments for operation. In order to energize the coil 20 for bright light headlamp operation, the valve means V may comprise a pair of electron flow relay tubes 27 and 28 respectively embodying a cathode 29 and 30, an anode 31 and 32, and a control grid 33 and 34. The anode 31 of the tube 27 may be connected with the A.C. conductor 24, the cathode 29 of said tube being connected to ground through a resistor 35 and with the A.C. conductor 25 through resistors 36 and 37, the interconnected ends of said resistors being also connected to ground through a resistor 38. The grid 33 of the tube 27 may be connected with one side of the detector 12, the other side of the detector being electrically connected with the interconnected ends of the resistors 36, 37 and 38.

The grid connected end of the detector 12 may also be connected with a resistance network comprising the thermistor T connected in parallel relation with a potentiometer 39, the adjustable contact element of which is connected through a resistor 40 with the grid connected side of the detector 12. One end of the thermistor T may be connected through a resistor 41 with the conductor 24, the other end of the thermistor being connected with the ground remote sideof the power source 14 through an adjustable ofiset resistor 42, the interconnected ends of the thermistor, the potentiometer 39 and the od set resistor 42 being electrically connected with the blade 19-of the switch 18.

The anode 32 of the tube 28 may be connected with the conductor 24 through the actuating coil 20 of the switch 18, a condenser 43 being connected across the opposite ends of said coil 20. The cathode 30 of the tube 28 may be connected to ground. The grid 34 of the tube 28 may be connected to ground through anormally open overriding switch 44; and said control grid may also be connected with the cathode 29 of the tube 27 through a resistor 45.

j In the absence of light incident upon the detector 12 at light dimming intensity, a positive potential will appear upon the grid 33 of the tube 27, thereby allowing the tube to deliver unidirectional current between its anode and cathode. As a consequence, a positive potential will appear upon the grid 34 of the tube 28, said grid 34 being connected with the cathode 29 of the tube 27 through the resistor 45. Such application of potential upon the grid 34 of the tube 28 will render the same conductive, thereby applying energizing current in the operating coil 20 of the relay 18 to condition the controlled vehicle lights for bright beam operation. When light from the headlights of an approaching vehicle impinges upon the crystal detector 12, its conductivity increases as a proportional function of the intensity of the impinging light, thereby decreasing the potential on the grid 33 whereby to con trol the tube 27 in fashion reducing the potential on the grid 34 of the tube 28.

The system may be conditioned so that, at a selected intensity of light impingement on the detector 12, the tube 27 will function to cause the tube 28 to become inoperative to energize the relay coil 20. As a consequence,

, the switch 18 will be thrown to its normal position in which the operating coil 17 of the switch 13 is disconnected from the power source 14, to thereby allow the switch blade 16 to connect the vehicle lamps for dim beam operation. When in position causing dim beam operation of the vehicle lamps, the switch 18 serves to short circuit the adjustable resistor 42 by connecting the interconnected ends of the potentiometer 39, the thermistor T,

and the adjustable resistance 39 with the ground remote side of the power source 14. The switch 18 thus operates to adjustthe voltage level applied upon the grid 33 of the tube 27 in a direction toward cutofi of current flow between the anode and cathode of the tube, thereby tending to prevent a return to bright light condition of the,

games a vehicle lamps in the event that the intensity of light'impinging upon the detector 12 becomes reduced as the as to'change the levelof potential applied on the grid 33 of the tube 27 in fashion to compensate for the potential "changing efiect of temperature upon the characteristics of the crystal detector 12. By closing the normally open overriding switch 44, the system may be disabled at any time, thereby conditioning the lamps for bright light operation regardless of .the intensity of light applied to the detector 12. The thermistor T preferably has a temperatureQcoeflicient of 4.4 percent per degree centigrade, and

. its resistance value, at 30 C., may be of the order of 30,000 ohms. The arrangement shown in Fig. l of the drawings is well adapted for temperature compensation down to temperatures of the order of 32 F.

in the arrangement shown in Fig. 2, the normally closed switch contact 15' may be connected with the low or dim beam filaments of the vehicle lamps, the contact 15 being adapted for connection with the high or bright beam lamp filaments. The switch actuating coil 17 maybe interconnected between the ground remote side of the power source 14 and the blade 19 of the switch 18, the movable pole 21 of said switch being electrically connected, with ground. Since said pole 21 is normally biased to engage with the switch blade 19, it will be seen that the actuating coil 17 of the switch 13 will be normally inactive with the low or dimmed beam lamp filaments in operation by the connection thereof with the power source through the switch blade 15' normally engaged by the pole 16 of the relay switch 13. By energizing theoperating coil 20 of the switch 18, its pole 21 will be released from the blade 19' and engaged with v the blade 19, to thereby energize the actuating coil 17 and cause the switch 13 to disable the low beam lamp filaments and energize the high beam lamp filaments for operation..

In order to energize the coil 20 for bright beam headlamp operation, the valve means V may comprise a pair of electron flow relay tubes 27 and 28', each respectively a resistor 38, the cathode 29 of the tube being connected with the shiftable contact element of a potentiometer 35', the resistance element of which is con nectedbetween the A.C. conductor 25 and the ground remote end of the resistor 38'. The control grid 33' may be connected with the shiftable contact element of a potentiometer 36', the resistance element of which is interconnected in parallel with a thermistor T between the A.C. conductor25 and a resistance 37' through which the thermistor and potentiometer may be connectedto ground. The anode 31' may be connected through a suitable resistor 39 to the control grid 34 of the tube 38'. The cathode 30' of the tube 28' may be connected to ground and its anode 32' may be connected j with the A.C. conductor 24 through the actuating coil 20 of the switch 18, a condenser 43 being connected across theopposite ends of said coil 20.

The anode 31' of the tube 27' may also be connected with the A.C. conductor 24 through the detector 12 and a resistor 41' disposed in series between said anode and said conductor, the detector connected end of the resistor 41' being interconnected with the blade 19 of the switch 18 through an adjustable offset resistor 42.

' When the system is in operation, the tube 27' will be in conductive condition, but current flow therethrough between anode and cathode will be a minimum in the ab- 'sence of light incident upon the detector 12 at light dimv embodying a cathode 129 and system is in operation, the voltage which appears at the anode of the pentode is applied through the resistor 39' to control the operation of the tube 28. This voltage is a function of the resistance of the pentode and is also a function of the impedance of the detector. It will fluctuate, therefore, in accordance with the thermal as well as photo responsive changes in the impedance of the detector. The thermistor is connected with the control grid of the pentode 'so that the effective resistance offered by the pentode may be changed as a function of temperature, as measured by the thermistor; and such alteration may be accomplished so as to offset or nullify the effect of the thermally sensitive impedance value of the detector on voltage applied to the grid of the tube 28.

As shown more particularly in Fig. 3 of the drawings, a full wave rectifier R may be interconnected between the conductors 24 and 25 in order to provide unidirectional current power for actuating the translation system 11, including the valve means V, said rectifier preferably comprising an electron flow tube having a cathode C and a pair of anodes respectively connected with the A.C. supply conductors 24 and 25, the cathode C being connected to ground through a condenser 46.

The switch member 15', which is normally engaged by the pole 16, may be connected with the low or dirn beam filaments of the vehicle lamps, the contact 15 being adapted for connection with the high or bright beam lamp filaments. The switch actuating coil '17 may be connected between the blade 19 of the switch 18 and the current remote side of the power source 14, the movable pole 21 of the switch being electrically connected to ground. Since said pole 21 is normally biased to a position engaging the switch blade 19' and disengaged from the switch 18, it willbe seen that the actuating coil 17 of the switch 13 will be normally inactive with the low or dim beam lamp filaments in operation, by connection thereof with the power source through the switch blade 15'. By energizing the operating coil 20 of the switch 18, its pole 21 will disengage the blade 19' and make contact with the blade 19, thereby energizing the actuating coil :17 and causing the switch 13 to disable the low beam lamp filaments and energize the high beam filaments for operation.

In order to energize the coil 20 for bright light headlamp operation, the valve means V may comprise a pair of electron flow relay tubes 127 and 128 respectively 130, an anode 131 and 134. The anode 131 of with the cathode of the 132, and a control grid 133 and the tube 127 may be connected rectifier through a resistor 135, the cathode 129 of said tube being connected to ground through a thermistor T. The grid 133 of the tube 127 may be connected to ground through a resistor 137. Said grid 133 may also be connected in series, through the detector 12 and a resistor 138, with an adjustable potential source. This source may conveniently comprise the movable contact of a potentiometer 139, the resistance component of which is connected between ground and one of the A.C. conduc tors, such as the conductor 24. A condenser 136 may be interconnected between ground and the detector connected end of the resistor 138.

The anode 132 of the tube 128 may be connected with one of the A.C. conductors, such as the conductor 25, through the actuating coil 20 of the switch 18,a condenser 43 being connected across the opposite ends of said coil 20. The cathode 130 of the tube 128 may be connected to ground. The grid 134 of the tube 128 may be connected to ground through a condenser 140; and said control grid may also be connected with translation means 141 for applying a control potential on the grid 134 of the tube 128, in response to the operation of the tube 127 under the control of the thermistor T and -'the detector 12.

The translation means 141 may comprise a detector may be connected to ground, as through a resistor 147,

i said control grid 146 being also connected with the anode 144 and, through a condenser 148, with the anode 149 of a detector tube 150, said tube 150 having a cathode 151 connected to ground, as through a resistor 152. The tube 150 may also have a control grid 153 connected to ground, as through a resistor 154, said grid 153 being also connected with the anode 131 of the tube 127, as through a condenser 155. The anode 149 of the tube 150 may be connected with the cathode 129 of the tube 127, as through a resistor 156, said anode 149 being also connected with the cathode C of the rectifier R, as through a resistor 157.

The tubes 127 and 150 form a two-stage voltage amplifier, the gain of which is controlled by the inverse feedback loop consisting of the resistor 137. The thermistor T is preferably one exhibiting a 4.4 percent change per degree centigrade, and having a resistance of the order of 10,000 ohms at C. It will be seen that the detector 12 is connected so that, in response to a the application of light upon the detector, it will modulate the carrier wave provided by the A.C. output of the transformer '22. This modulated carrier is then amplified by the feedback amplifier, comprising the tubes 127 and 15%), the feedback loop of which amplifier serves to alter the gain of the amplifier in such a fashion that amplifier output is essentially independent of temperature for all intensity levels of light, as applied on the detector 12.

To actuate the relay 18, the signal delivered from the amplifier is detected by the peak reading detector tube 142, the output of which is arranged to control the operation of the relay tube 128. The circuitry is such that the system warms up for operation when the switch 13 is in the low beam position, and becomes effective to energize the coil 20 in the absence of light on the detector at lamp dimming intensity, the system functioning to deenergize the actuating coil 20 of the switch 18, as and when light at or above lamp dimming intensity impinges upon the detector 12.

Offset is accomplished by altering the load resistance at the input of the amplifier, as by connecting the blade 19 of the switch 18 with the control grid 133 of the tube 127 through a resistor 158, said grid being also connected to ground, as through a condenser 159. The grid 133 thus is connected to ground through the resistor 137, at all times, and is connected to ground through the resistors 137 and 138, in parallel relationship, whenever and so long as the switch pole 21 engages the blade 19, when the switch actuating coil 20 is deenergized, that is to say, when the system is conditioned for dim light operation. The system shown in Fig. 3 of the drawings is well adapted for temperature compensation, down to temperatures of the order of 22 F.

It is thought that the invention and its numerous attendant advantages vw'll be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit and of its attendant advantages, the forms herein disclosed being preferred embodiments for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

1. Control apparatus comprising an electrical power operable device, a photosensitive semi-conductor selected from the class consisting of the sulphides and selenides of cadmium and mercuryand forming a detector that is also thermally responsive, relay means for controlling scope of the invention, or sacrificing anyv the delivery of operating power to the controlled device, means for controlling the operation'of said relay means in response to changes in the impedance value of said detector, and a thermistor connected with said relay means for modulating the operation thereof in accordance with changes in ambient temperature in the vicinity of the detector, whereby to nullify the effect of thermally responsive changes in the impedance of the detector upon the operation of the controlled device.

2. Control apparatus as set forth in claim 1, wherein said relay means comprises an electron flo w valve having anode, cathode and control grid components, and circuit means connecting the detector and the thermistor with a said component.

3. Control apparatus, as set forth in claim 1, wherein said relay means comprises an electron flow 'valve having anode, cathode and control grid components, and circuit means electrically connecting said thermistor and said detectorwith the control grid of said valve.

4. Control apparatus as set forth in claim 1, wherein said relay means comprises an electron flow valve having anode, cathode and control grid components, and circuit means electrically connecting said thermistor with one of said components and the detector with another of said components.

5. Control apparatus as set forth in claim 1, wherein said relay means comprises an electron flow valve having anode, cathode and control grid components, and circuit means electrically connecting the detector with said anode component and the thermistor with another of said components.

6. Control apparatus as set forth in claim 1, wherein said relay means comprises an electron flow valve having anode, cathode and control grid components, and circuit means electrically connecting said thermistor with the grid component and the detector with another of said components.

7. Control apparatus as set forth in claim 1, wherein said relay means comprises an electron flow valve having anode, cathode and control grid components, and circuit means electrically connecting the thermistor with said cathode component and the detector with another of said components.

8. Control apparatus for vehicle headlights comprising an electrical power operable relay switch for conditioning the vehicle headlights selectively for bright and dim beam operation, a photosensitive semi-conductor selected from the class consisting of the surpbides and selenides of cadmium and mercury and forming a detector that is also thermally responsive, relay means for controlling the delivery of operating power to the relay switch, means for controlling the operation of said relay means in response to changes in the impedance value of said detector, and a thermistor connected with said relay means for modulating the operation thereof in accordance with changes in ambient temperature in the vicinity of the detector, whereby to nullify the effect of thermally responsive changes in the impedance of the detector upon the operation of the relay switch.

9. Control apparatus for vehicle headlights comprising an electrical power operable relay switch for conditioning the vehicle headlights selectively for bright and dim beam operation, a photosensitive semi-conductor selected from the class consisting of the sulphides and selenides of cadmium and mercury and forming a detector that is also thermally responsive and disposed in position to receive the impingement thereon of light rays emitted by the headlamps of an approaching vehicle, relay means embodying an electron flow valve for controlling the delivery of operating power to said relay switch, said detector being connected with said electron flow valve to control the operation of said relay means in response to changes in the impedance of said detector, and a thermistor disposed near the detector and connected with said valve for modulating the operation in accordance with ambient temperature in the vicinity of the detector, to thereby control the operation of the relay switch in fashion nullifying the relay controlling effect of thermally induced changes in the impedance of the detector.

References Cited in the file of this patent UNITED STATES PATENTS 1,694,511 Von der Lippe-Lipski Dec. 11, 1928 1,745,149 Carney Jan. 28, 1930 2,562,538 Dyer July 31, 1951 2,614,227 Bordewieck et a1. Oct. 4, 1952 2,742,592 Miller et al Apr. 17, 1956 2,806,180 Falge et al. Sept. 10, 1957 2,807,752 Mcllvaine Sept. 24, 1957 FOREIGN PATENTS 369,546 Great Britain Sept. 16, 1932 

